Observation of direction instability in a fiber ring laser

Abstract

We report on the observation of a new phenomenon occurring in a fiber ring laser. This phenomenon is about the transition from an initially bidirectional emission of a reciprocal fiber ring laser to a unidirectional emission at a certain pump power threshold. In addition, the final direction is not predefined but appears to be randomly chosen every time the threshold is exceeded. Therefore, we term this new phenomenon direction instability. Furthermore, we provide a first discussion of how the instability threshold is influenced by the length and the loss of the cavity. We show that the threshold follows a power times length scaling, indicating a nonlinear origin.

Figure 1

General scheme of the all-fiber ring laser. The setup consists of a pump diode (pump), pump signal combiner (PSC), an active Yb-doped fiber (Yb), a passive Ge-doped fiber (Ge), and an output coupler (OC). The output signal is monitored by an optical spectrum analyzer (OSA) and a power meter (PM).

Figure 2

General evolution of (a) the combined output power and (b) the directional output powers demonstrating a bistability and unidirectional lasing behavior.

Figure 3

General example for the spectral evolution of the final direction output during increase of pump power starting at the laser wavelength around 1100 nm and broadening by 6 Stokes Raman orders and additional wavelength components up to 1700 nm.

Figure 4

Attenuation as a function of wavelength for the two versions of Corning’s HI1060 fiber. The inset highlights the region of the laser wavelength.

Figure 5

DI threshold power as a function of passive fiber length and loss. The inset highlights the power difference between two trends.

Figure 6

Output power as a function of increasing pump power separated in runs where the cavity switched to (a) the clockwise and (b) the counterclockwise direction. There are 30 runs in total. The cavity contained 2 km high loss fiber V2.

Figure 7

Superimposed output power traces for 30 power cycles of the cavity containing 1 km low loss fiber separated in switching events during (a) increase and (b) decrease of the pump power, or (c) without switching to unidirectional lasing.

Figure 8

Detailed plots regarding the output power behavior for switching events happening (a) during power increase, (b) during power decrease, or (c) not at all. Regions with a fluctuating power trend are highlighted in red and with smooth trend in green.